Conventionally, an electrophotographic-type image forming apparatus is known that is provided with an exposing device that exposes a photosensitive member with laser light. The exposing device includes a laser diode, a polygon mirror, a polygon motor, and the like. The exposing device deflects laser light emitted from the laser diode by the polygon mirror, another mirror, a lens, etc. and scans a surface of the photosensitive member for exposure. Here, the exposing device blinks laser light in accordance with an image to be printed, thereby exposing the surface of the photosensitive member so that an electrostatic latent image corresponding to the image is formed on the surface.